In the field of wireless communications, particularly in a cellular mobile communications network, uplink data transmission from a terminal device to a base station may be performed by using a contention-based uplink transmission mode. The terminal device selects an available uplink resource from a preallocated uplink resource pool, to transmit data to the base station. After receiving the uplink data sent by the terminal device, the base station needs to feed back acknowledgement information to the terminal device, to notify the terminal device whether the sent data is correctly received.
The base station determines, based on a location of the uplink resource used by the terminal device, a location of a downlink resource used for feeding back the acknowledgement information to the terminal device. When at least two the terminal devices simultaneously select a same uplink resource for transmission, in other words, there is a transmission conflict, the base station uses a same downlink resource to feed back the acknowledgement information. However, when the base station needs to feed back different acknowledgement information to terminal devices, use of a same downlink resource causes some of the terminal devices to receive incorrect acknowledgement information, resulting in a logic error.